I am not clearly about it but typically one server has one database (with many users), if you create many databases mean that you create many instances, listeners, ... as well. So you can check your LISTENER to identify it.
In my testing I created 2 databases (dbtest and dbtest_1) so when I check my LISTENER status it appeared like this:
lsnrctl status
....
STATUS of the LISTENER
.....
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=10.10.20.20)(PORT=1521)))
Services Summary...
Service "dbtest" has 1 instance(s).
Instance "dbtest", status READY, has 1 handler(s) for this service...
Service "dbtest1XDB" has 1 instance(s).
Instance "dbtest1", status READY, has 1 handler(s) for this service...
Service "dbtest_1" has 1 instance(s).
Instance "dbtest1", status READY, has 1 handler(s) for this service... The command completed successfully